Now celebrity chef rocco DiSPIRITO HAS A BRAND-NEW BOOK With a new plan to help you shed weight fast called the pound a day diet and our sarah haines followed one woman as she tried to lose five pounds in five days. Low fat -- CELEBRITY CHEF rocco DiSpirito whips up delicious meals. Very good. Reporter: But now he says he's created a diet where you can eat what you love and lose weight. The goal of his new book, to help dieters lose five pounds in five days. I don't like the way clothes fit on me even when I can get them on. Reporter:43-year-old lisa dell pore to has been 43 pounds heavi heavier. She's following rocco's diet which turs your body into a fat burning machine. In phase one you consume lots of water, pack your weight in ones every day along with six small protein-packed meals, 850 calories a day. More on the weekend. For a month. Then phase two starts. You get to eat more but learn to keep the weight off for life. I got to check this out. Hello. Reporter: We met up in brooklyn, new york. How is this diet difference? It's delicious. These recipes are easy to make. Taste great and a chef's point of view that's been missing is health. Reporter: Don't have time to cook? No problem. You can do my 28-day phase one with store bought food if you really want to. Reporter: Part of the diet's appeal is quick weight loss so dieters feel motivated they're on the right track but experts say in some cases rapid weight loss can actually be dangerous. Electrolyte abnormality, cardiac consequences and multiple other medical issues. Reporter: Rocco maintains his diet is safe created with the help from a doctor and filled with micro nutrients that other aggressive diets may lack and lisa on day two says the diet is working. I literally lost three pounds in two days. Reporter: One of the staples of his plan is a morning chocolate shake. So, rocco, what is this smoothie I've heard about. A chocolate smoothie, 30 grams of protein. It'll last throughout the whole day. Reporter: We adjust six ingredients including dark unsweetened cocoa and ice.O cf1 o you could add more ice if you like it churchier. We can double up on the ice if you want to. Reporter: You can make that tweak later. There's no milk, no sugar. Can rocco hook us up with a delicious smoothie. How does it -- how does it taste. Like a cup of chocolate. As for lisa, day five, not only has she lost 4.7 pounds but an inch and a half off her waist. I'm very excited. Reporter: For "good morning america," sara haines, abc news, new york. You know another way to get

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